Fault tolerance in wireless networks

ABSTRACT

A network includes a plurality of logical access entities. Each access entity includes two or more communication interfaces. The network further includes a plurality of logical node entities. Each logical node entity includes two or more communication interfaces that are configured to wirelessly communicate in a redundant manner with any of the logical access entities. In an embodiment, a communication degradation in the network is assessed, and the network is configured as a function of that assessment to provide fault tolerance within the network.

RELATED APPLICATIONS

This application is a continuation of U.S. Serial application Ser. No.11/604,637, which was filed on Nov. 27, 2006, and which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

Various embodiments relate to networks, and in an embodiment, but not byway of limitation, to fault tolerance in wireless networks.

BACKGROUND

The availability of wireless networks has increased tremendously overthe last decade or so. Wireless networks offer, among other features,increased convenience to its users. One example of a wireless network isan 802.11x based network.

The basic architecture of an 802.11x based network is shown in FIG. 1.The basic building blocks of 802.11x based networks are referred to asBasic Service Sets (BSS). The BSS consists of an Access Point (AP) orsimilar logical access entity with several nodes, stations, or otherlogical node entities wirelessly connected to it. Because of thelimitations in the physical layer, the direct node to node distance thatmay be supported is limited. To overcome this limitation, several BSSsmay come together to form an extended network. This interconnection isbasically done using the distribution system (DS) as shown in FIG. 1,and 802.11x logically separates the wireless medium from theDistribution System Medium (DSM). The DS and the BSS can be leveraged tocreate larger networks referred to as Extended Service Sets (ESS). TheLogical Link Control (LLC) views the ESS as an independent or single BSS(IBSS) network. Nodes within an ESS may communicate with each other andthey may move from one BSS to another, and this movement is transparentto the LLC.

While an 802.11x network and other wireless network protocols permitmuch flexibility in their use, and support bandwidths ranging from a fewKbps to tens of Mbps, issues still remain related to the robustness andreliability of these wireless networks. Wireless networks would thusbenefit from protocols and architectures that address robustness andreliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example embodiment of master-slave wirelessnetwork.

FIG. 2 is a table listing possible modes in which faults may arise intypical wireless networks.

FIG. 3 is a table listing possible redundancies that can be provided toovercome the various failure modes listed in FIG. 2, for a master-slavewireless network as depicted in FIG. 1.

FIGS. 4-10 illustrate example embodiments of fault tolerantarchitectures of wireless networks.

FIG. 11 illustrates an example embodiment of a fault tolerantarchitecture of a wireless network.

FIG. 12 illustrates a flowchart of an example embodiment of a process toprovide a wireless network with fault tolerance.

FIG. 13 illustrates an example embodiment of a computer architecture inconnection with which one or more embodiments of the present disclosuremay operate.

SUMMARY

A network includes a plurality of logical access entities. Each accessentity includes one or more communication interfaces. The networkfurther includes a plurality of logical node entities. Each logical nodeentity includes one or more communication interfaces that are configuredto wirelessly communicate in a redundant manner with any of the logicalaccess entities. In an embodiment, a communication degradation in thenetwork is assessed, and the network is configured as a function of thatassessment to provide fault tolerance within the network.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different, are not necessarilymutually exclusive. Furthermore, a particular feature, structure, orcharacteristic described herein in connection with one embodiment may beimplemented within other embodiments without departing from the scope ofthe invention. In addition, it is to be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the scope of the invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims, appropriately interpreted, along with the fullrange of equivalents to which the claims are entitled. In the drawings,like numerals refer to the same or similar functionality throughout theseveral views.

Embodiments of the invention include features, methods or processesembodied within machine-executable instructions provided by amachine-readable medium. A machine-readable medium includes anymechanism which provides (i.e., stores and/or transmits) information ina form accessible by a machine (e.g., a computer, a network device, apersonal digital assistant, manufacturing tool, any device with a set ofone or more processors, etc.). In an exemplary embodiment, amachine-readable medium includes volatile and/or non-volatile media(e.g., read only memory (ROM), random access memory (RAM), magnetic diskstorage media, optical storage media, flash memory devices, etc.), aswell as electrical, optical, acoustical or other form of propagatedsignals (e.g., carrier waves, infrared signals, digital signals, etc.).

Such instructions are utilized to cause a general or special purposeprocessor, programmed with the instructions, to perform methods orprocesses of the embodiments of the invention. Alternatively, thefeatures or operations of embodiments of the invention are performed byspecific hardware components which contain hard-wired logic forperforming the operations, or by any combination of programmed dataprocessing components and specific hardware components. Embodiments ofthe invention include digital/analog signal processing systems,software, data processing hardware, data processing system-implementedmethods, and various processing operations, further described herein.

A number of figures show block diagrams of systems and apparatus ofembodiments of the invention. A number of figures show flow diagramsillustrating systems and apparatus for such embodiments. The operationsof the flow diagrams will be described with references to thesystems/apparatuses shown in the block diagrams. However, it should beunderstood that the operations of the flow diagrams could be performedby embodiments of systems and apparatus other than those discussed withreference to the block diagrams, and embodiments discussed withreference to the systems/apparatus could perform operations differentthan those discussed with reference to the flow diagrams.

One or more embodiments of the present disclosure provide a faulttolerant wireless network. Consequently, wireless networks that are morerobust and reliable may be installed and/or deployed.

In one or more embodiments, modifications are made to wirelessarchitectures known in the art to make those wireless networks morerobust and resilient to communication degradations. The modified systemsand networks are capable of identifying failure states arising due tocommunication degradation factors, and thus make these systems andnetworks tolerant to these faults when they occur. While in thisdisclosure the well known IEEE 802.11x WLAN standard in a master-slavemode is used as an example, the present disclosure may easily be appliedto other wireless networks that operate in master-slave mode orhierarchical mode and support multiple non-overlapping channels andmultiple accesses on the same channel (like Code Division MultipleAccess (CDMA) or Time Division Multiple Access (TDMA)).

It is well known that due to the fundamental nature of a medium inwireless networks the transmission characteristics arenon-deterministic. Due to this inherent drawback, the wirelesscommunication link is susceptible to failures, thus making itunreliable. The received signal strength in such wireless networksdepends on several factors such as channel interference, signal fading,and reflecting obstructions, just to name a few. Apart from this, thereare several other factors that add to the unreliable nature of thecommunication channel such as congestion in the link (due to otherwireless systems that coexist in the same frequency spectrum or othernodes contending for the channel), or failure of the Access Points (APs)and interface devices. It is noteworthy that one of the resulting statesof communication degradation in wireless networks is thesystem/sub-system failure.

An embodiment approaches these reliability and robustness problems byincorporating consequential awareness in the system/network with respectto the failure modes arising due to communication degradation, providesmethods for fault identification, and thus induces fault tolerance intothe system.

The fault tolerance approaches of this disclosure address such issues aslink failure, AP failure, failure of the wireless interface on AP andwireless nodes, and tolerance to congestion in the links, just to name afew. These issues are addressed in several manners including pathdiversity, channel and link diversity, data diversity, AP diversity, andinterface diversity, which result in various architectural alternativesthat achieve robust and fault resilient wireless communication networks.

FIG. 2 is a table of possible modes in which faults may arise in typicalwireless networks, such as the example network depicted in FIG. 1. FIG.2 lists potential sub-system failures, the possible causes of thesesub-system failures, and the impact of these failures on thecommunication between sub-systems. With reference to FIG. 1, typicalsub-systems of wireless networks would be an AP (master), a wirelessnode (slave node), and the communication between the master and slavenodes. The several approaches and techniques described herein addressone or more of the failure modes outlined in FIG. 2.

The present disclosure incorporates features such as consequentialawareness of communication degradation amongst the sub-systems inwireless networks and also provides techniques to tolerate relatedfailures. That is, an architecture is disclosed that provides thecapability to identify a degradation of communication in a wirelessnetwork. The architecture further provides for fault tolerance and faultavoidance in the event of a sub-system failure.

In one or more embodiments, such fault tolerance is achieved throughredundancy. For example, there may be link or channel redundancy betweenthe APs and the wireless nodes, redundancy of the APs, and redundancy ofnetwork interface cards (NIC) on the nodes and the APs. A combination ofall of these are illustrated in FIG. 3, and result in a variety ofoptions, each one of which results in a different level of robustnessand fault resilience. Other features of fault avoidance andcommunication degradation awareness are provided through middleware,which is a software algorithm that exists on the wireless nodes in thesystem.

Referring to FIG. 3, the various possible failure modes are interfacefailures (NIC card failures on both APs and Nodes), link failure betweenthe nodes and APs, communication channel corruption between the nodesand the APs, data losses, and congestion over the links between the APsand nodes. A combination of the various features listed across the topof FIG. 3 (Node with 1 NIC, Node with 2 NICs, etc.) results in differentarchitectures which address the various failure modes.

Option 3 in FIG. 3 is illustrated in diagrammatic form in FIG. 4. FIG. 4illustrates a portion of a network 400 including a distribution system410, access points 420 and 425, and nodes 430 and 435. The access points420 and 425 may be referred to as logical access entities, and the nodes430 and 435 may be referred to as logical node entities. The accesspoints and the nodes may both be referred to as logical communicationentities. Each access point has a first NIC 421, 422 and a second NIC423, 424. Each node has a single NIC 432, 433. The NICs may also bereferred to as communication interfaces. Consequently, every wirelessnode is equipped with only one NIC, whereas the access points areequipped with a primary NIC and a secondary NIC. This architectureaddresses the issue of failure of the NIC on the APs. The two NICs onany AP can operate over the same frequency channel or on differentchannels. The two nodes in this architecture communicate with each otherover the DS. The available (redundant) paths between node 430 and 435include the following:

Path1: Node430→AP NIC 421→AP NIC 422→Node 435

Path2: Node430→AP NIC 421→AP NIC 424→Node 435

Path3: Node430→AP NIC 423→AP NIC 422→Node 435

Path4: Node430→AP NIC 423→AP NIC 424→Node 435

FIG. 5 illustrates option 4 from the table in FIG. 3. Like in FIG. 4,each access point 420 and 425 have two NICs 421, 423 and 422, 424respectively. Similarly, each node 430 and 435 have a single NIC 432 and433 respectively. The APs 420 and 425 in FIG. 5 act as redundant APs inthe sense that their coverage areas intersect with one another, i.e. theBSSs of access point 420 and access point 425 overlap each other. Thearchitecture of FIG. 5 provides tolerance to AP failure and also tofaults arising due to the failure of the NICs on the APs. This approachalso handles the situation arising due to the failure of thecommunication channel between the APs and the nodes. Like thearchitecture of FIG. 4, the two NICs on the APs might operate either onthe same channel or on different channels.

As shown in FIG. 5, both the NICs 421 and 423 on AP 420, and NICs 422and 424 on the AP 425, can operate on two non-overlapping channels. Thenodes 430, 435 can associate to their preferred AP over these channels(preferably the nodes 430, 435 should operate on non-overlappingchannels). In the event of a failure of one of the APs 420, 425, thenodes associated with that AP can switch to the redundant AP on the samechannel. This is illustrated by the dashed lines 465A, 465B in FIG. 5.Another option for the node in the event of a failure of its preferredAP is to switch its operating frequency to the other non-overlappingchannel and associate itself with the redundant AP (as shown by thedash-dot lines 466A, 466B in FIG. 5). In the event that one of the NICson its preferred AP fails, the node can switch its operating channel andassociate with the redundant NIC of its preferred AP operating overanother channel as shown by the dotted lines 460A, 460B in FIG. 5.

Thus, utilizing the approach in FIG. 5, the various possible pathsbetween node 430 and node 435 include:

Path1: Node430→AP NIC 421→AP NIC 422→Node 435

Path2: Node430→AP NIC 421→AP NIC 424→Node 435

Path3: Node430→AP NIC 423→AP NIC 422→Node 435

Path4: Node430→AP NIC 423→AP NIC 424→Node 435

Path5: Node430→AP NIC 422→Node 435

Path6: Node430→AP NIC 424→Node 435

Path7: Node430→AP NIC 421→Node 435

Path8: Node430→AP NIC 423→Node 435

Another approach is given by option 5 in FIG. 3. In Option 5, each APhas only one NIC, while on the other hand the nodes are equipped withdual NICs—one referred to as a primary NIC and the other referred to asa secondary NIC. This is illustrated in FIG. 6. The secondary NIC takesover the functionality of the primary NIC in the event of failure of theprimary NIC. This approach provides node level link diversity and nodeNIC diversity. The different paths between node 430 and node 435 includethe following:

Path1: Node430 NIC 431→AP NIC 421→AP NIC 422→Node 435 NIC 432

Path2: Node430 NIC 431→AP NIC 421→AP NIC 422→Node 435 NIC 434

Path3: Node430 NIC 433→AP NIC 421→AP NIC 422→Node 435 NIC 432

Path4: Node430 NIC 433→AP NIC 421→AP NIC 422→Node 435 NIC 434

In another embodiment, a redundant APs concept is disclosed (option 6 inFIG. 3) with the APs' BSSs intersecting so that the nodes would be ableto communicate with both the APs as shown in FIG. 7. This embodimentprovides tolerance to faults arising due to failure of NICs on thenodes, failure of APS, and also provides data replication opportunity.Duplicate packet management can be taken up at the upper layers. In thisembodiment, the different paths between nodes 430 and node 435 wouldinclude the following:

Path1: Node430 NIC 431→AP NIC 421→AP NIC 422→Node 435 NIC 432

Path2: Node430 NIC 431→AP NIC 421→AP NIC 422→Node 435 NIC 434

Path3: Node430 NIC 433→AP NIC 421→AP NIC 422→Node 435 NIC 432

Path4: Node430 NIC 433→AP NIC 421→AP NIC 422→Node 435 NIC 434

Path5: Node430 NIC 431→AP NIC 422→Node 435 NIC 432

Path6: Node430 NIC 431→AP NIC 422→Node 435 NIC 434

Path7: Node430 NIC 433→AP NIC 421→Node 435 NIC 432

Path8: Node430 NIC433→AP NIC 421→Node 435 NIC 434

The NICs on the two APs would preferably be operating on non-overlappingchannels. The redundant NICs on the nodes can be associated with twodifferent APs as their coverage areas overlap as shown in FIG. 7. Thedashed and the dotted lines show the other options available in theevent of the failure of the NIC on the node and the AP failuresrespectively.

In the embodiments of option 7 and option 8 of FIG. 3, any given node isassociated with more than one AP over non-overlapping channels. Thebasic topological assumption here is that the BSSs partially overlap andalso the IBSS and ESS networks can co-exist in the same physical spacewith other ESS networks. Every node intended to maintain link redundancywill have redundant NICs (i.e., two separate cards). Each of these NICcards is associated with different APs. In this embodiment, any faulttolerant node (i.e., a node with two NICs) would have two communicationlinks. Also, the APs are provided with dual interfaces that are used tocommunicate with the fault tolerant nodes. Both of these interfaces onthe APs can operate simultaneously over two non-overlapping channels.

One manner of realizing the ideas represented by option 7 in FIG. 3 isthat every node and AP has two wireless interfaces that are beneficiallyoperating on non-overlapping channels as shown in FIG. 8. As shown inFIG. 8 (which covers option 7), both interfaces of the nodes areassociated with the respective interfaces of the AP. There are at leasttwo ways in which this embodiment can be implemented. First, both thecommunication links are active (both interfaces of the nodes and APs).The node transmits its packets on both of these links. However, theduplicate packet management can be done either by the AP or it can bedone at the upper layers as well. Second, only one communication link(so called the primary link) can be active at a time and the other link(so called the secondary) is activated only in the event of the failureof the primary link. However, the channel frequency for communication bythe APs and the nodes is decided beforehand. This embodiment providestolerance to faults arising from link availability, channel congestion,and NIC card failure on either the AP or on the node. However, it doesnot address the issue of AP failure. In this embodiment, there are fourpaths between any two fault tolerant nodes. Therefore, referring againto FIG. 8, the different paths existing between nodes 430 and 435,include:

Path1: Node430 NIC 431→AP 420 NIC 421→AP 425 NIC 422→Node 435 NIC 432

Path2: Node430 NIC 431→AP 420 NIC 421→AP 425 NIC 424→Node 435 NIC 434

Path3: Node430 NIC 433→AP 420 NIC 423→AP 425 NIC 422→Node 435 NIC 432

Path4: Node430 NIC 433→AP 420 NIC 423→AP 425 NIC 424→Node 435 NIC 434

Similarly, two paths exist between a fault tolerant node and a non-faulttolerant node. Specifically, referring to FIG. 8, the paths between node435 and node 440 are as follows:

Path1: Node435 NIC 432→AP 425 NIC 422→AP 425 NIC 424→Node 440 NIC 442

Path2: Node435 NIC 434→AP 425 NIC 424→Node 440 NIC 442

It is noteworthy that a non-fault tolerant node is authenticated orassociated to only one AP at any given point in time. However, ashortcoming of this embodiment is that it cannot address AP failure.However, if the architecture incorporates overlapping BSS's, even the APfailure can be handled.

In order to cover AP failure under the purview of fault tolerance, anarchitecture such as that illustrated in FIG. 9 may be implemented(Option No. 8 in FIG. 3). In this embodiment, the fault tolerant nodesare associated with different APs via different interfaces (whichpreferably operate over non-overlapping channels). The fault tolerantnodes are in the coverage of both the APs. To achieve better faulttolerance, one interface of a node is associated with one AP using oneof the channels and the other interface of the same node is associatedwith another AP on a channel which is non-overlapping with the firstinterface. Consequently, even if one of the APs fails, the node canstill communicate with the rest of the network through its communicationlink with another AP.

In the event of a failure of both the links of a node with respectiveAPs, the interfaces will re-associate with the interfaces of other APson corresponding channels. This is shown in FIG. 9 by the dashed lines.The interface cards are pre-authenticated with the corresponding channelof another AP during initialization phase. This assists in reducing there-association time with that channel. In this embodiment, all the NICsof the nodes and the APs are functionally active all the time. Thisembodiment is tolerant to faults induced due to failure of the link(path diversity), congestion on the link, failure of NICs on APs/nodes(frequency diversity), and also the failure of the APs themselves. Inthis embodiment, eight paths exist between any two fault tolerant nodes.As illustrated in FIG. 9, the existing paths between node 430 and node435 are as follows:

Path1: Node430 NIC 431→AP 420 NIC 421→AP 425 NIC 422→Node 435 NIC 432

Path2: Node430 NIC 431→AP 420 NIC 421→AP 425 NIC 424→Node 435 NIC 434

Path3: Node430 NIC 431→AP 420 NIC 421→AP 420 NIC 423→Node 435 NIC 434

Path4: Node430 NIC 431→AP 420 NIC 421→Node 435 NIC 432

Path5: Node430 NIC 433→AP 420 NIC 423→Node 435 NIC 434

Path6: Node430 NIC 433→AP 420 NIC 423→AP 425 NIC 424→Node 435 NIC 434

Path7: Node430 NIC 433→AP 420 NIC 423→AP 425 NIC 422→Node 435 NIC 432

Path8: Node430 NIC 433→AP 420 NIC 423→AP 420 NIC 421→Node 435 NIC 432

Similarly, between a fault tolerant node and a non-fault tolerant node,four paths exist. For example, the available paths between node 435 andnode 440 are as follows:

Path1: Node435 NIC 432→AP 420 NIC 421→AP 425 NIC 424→Node 440 NIC 442

Path2: Node435 NIC 432→AP 425 NIC 422→AP 425 NIC 424→Node 440 NIC 442

Path3: Node435 NIC 434→AP 425 NIC 424→Node 440 NIC 442

Path4: Node435 NIC 434→AP 420 NIC 423→AP 425 NIC 424→Node 440 NIC 442

One of the advantages to this embodiment is the degree to which thefault tolerance is provided. As depicted above, eight different pathsare available between any two fault tolerant nodes. Also, the scenariosof AP failure are taken care of in this embodiment. However, anassociated disadvantage could be the fact that all the four NICs (twoeach on AP and the fault tolerant nodes) are active at any given pointin time. Because of this, two APs would be operating on two identicalchannels (interfaces 1 of AP1 and AP2 and also interfaces 2 of AP1 andAP2, similarly the interfaces on the wireless nodes) which may reducethe number of nodes that can be operated in that region over thoseparticular channels. This is due to the fact that two identical channelsare operational in the same region/physical space that is contended forby the devices belonging to the respective channels.

An embodiment that may overcome the disadvantage of the previousarchitecture is illustrated in FIG. 10. The architecture in FIG. 10 issimilar to the architecture in FIG. 9 except that in FIG. 10 all theNICs of an AP are not functioning at the same time. That is, one of theNICs is active while the other NIC is inactive. As shown in FIG. 10,interface 1 (NIC 421) of AP 420 is active while interface 2 (NIC 423) isinactive and for AP 425 interface 2 (NIC 424) is active whereasinterface 1 (NIC 422) is inactive (wherein the inactive status is shownby dotted lines). The inactive channel (which is preferablynon-overlapping with respect to the other NICs on that AP) of APs getsactivated only if the corresponding channel of the other AP fails. Therehas to be a mechanism provided in the APs which determines this failureof channel and intimates the other APs to activate the correspondingchannel. Initially, when the node gets associated with the two APs, thenode decides its preferred link by comparing the link quality of the twolinks. This embodiment provides tolerance to faults induced due tofailure of the link, congestion over the link, failure of the NICs onthe APs and nodes, and also the failure of the APs. In this embodiment,since only one of the two interfaces on each device (node and AP) isactive, effectively only 4 (out of the maximum of 8) paths exist betweenany two fault tolerant nodes. Referring to FIG. 10, the paths betweennode 430 and node 435 are as follows:

Path1: Node430 NIC 431→AP 420 NIC 421→Node 435 NIC 432

Path2: Node430 NIC 431→AP 420 NIC 421→AP 425 NIC 424→Node 435 NIC 434

Path3: Node430 NIC 433→AP 425 NIC 424→Node 435 NIC 434

Path4: Node430 NIC 433→AP 425 NIC 424→AP 420 NIC 421→Node 430 NIC 431

Similarly, two paths exist between a fault tolerant node and a non-faulttolerant node. Referring again to FIG. 10, the paths between node 435and node 440 are as follows:

Path1: Node435 NIC 432→AP 420 NIC 421→AP 425 NIC 424→Node 440 NIC 442

Path2: Node435 NIC 434→AP 425 NIC 424→Node 440 NIC 442

As it is evident, this embodiment addresses the disadvantages of theembodiments of FIGS. 8 and 9. A disadvantage of the embodiment of FIG.10 might be the activation of redundant NICs in the event of a failure.This might add to the delay in communication. Thus, the choice among thedifferent embodiments can be made based on the degree of fault tolerancedesired in the system. For example, if an application is designed thatdemands link diversity on both the APs and the nodes, and also demandsAP diversity, option no. 8 in FIG. 3 would be appropriate. A combinationof these basic fault tolerant options would result in several hybridarchitectures which increases the scope of the fault tolerance providedto the networks.

In the present disclosure, middleware that resides on top of the mediumaccess control (MAC) layer of the nodes and APs is disclosed, and therole of the middleware is to monitor the health of the link and channelfor each of the network interfaces on the device, put the packets ondesired interfaces (depending on whether data is transmitted on both theinterfaces or only one interface), and eliminate the duplicate packetswhen both the network interfaces are working (only in case of APs). Onthe other hand, if only one network interface is working at any point intime, the middleware performs the job of switching between the networkinterfaces based on the link quality. Thus, the middleware monitors thehealth of the link/channel associated with each network interface beforetaking any decisions regarding transmission of data on those interfaces.Similarly, the middleware on the AP also shares the link qualityinformation with the other APs so that in the event of its failure, theredundant AP can take charge of the network.

The above disclosure and description focus on achieving fault tolerancethrough dual redundancy (with two NICs on APs and nodes and differentvariants of the same). However, the disclosure is not limited, and theconcept can be extended to n-level redundancy.

In order to achieve the desired fault tolerant properties explainedabove, the architecture of the fault tolerant nodes should be modifiedslightly as illustrated in FIG. 11. There is a physical layer 1150, andon top of the MAC layer 1140, there is a fault tolerant layer 1110 thatincludes two blocks—link fault detector 1120 (LFD) and the link switchover 1130 (LSO) components. The LSO may include a path switchover 1132and/or a communication channel switchover 1134. The LFD 1120 isprimarily used to detect the non-availability of the given communicationlink. The LFD 1120 can perform this task based on any combination of thefollowing options. It is noted that are some of the options for the LFD1120 to operate. The list can nevertheless be exhaustive.

-   -   1. Received Signal Strength Indication (RSSI)—This can be a good        measure for the link health since it acknowledges the presence        of noise or interference in the operating channel.    -   2. Sudden drop in SNR value of the link—Signal strength of a        signal from an AP is available at the lower layer of the        protocol stack. From the signal strength, the SNR value can be        determined in decibels. Sudden drop in the SNR value can be an        indication of link or channel failure.    -   3. The number of packets waiting for the medium in the        transmission/re-transmission queue.    -   4. The total number of re-transmissions—This could be a measure        to identify AP failure or congestion in the channel.    -   5. The number of acknowledgment packet failures observed by the        transmitting nodes indicate the possibility of either channel        failure or AP failure.

Based on these observations, once the LFD 1120 determines that the givenlink is unusable, the LSO 1130 switches over to the redundant link basedon the architecture alternatives in the disclosed embodiments. The faulttolerant layer 1110 in association with 1120 and 1130 as shown in FIG.11 may perform the following functionalities:

-   -   1. The middle layer may control the initial association process.        That is, it has to make sure that the two NIC cards are        associating with two different APs over two non-overlapping        channels so that maximum fault tolerance can be achieved.    -   2. It should have the fault detection mechanism to detect all        the possible failure modes listed in FIG. 2 and communicate the        same to the operator.    -   3. In the event of a failure, the middleware should be capable        of switching the traffic to the backup link without affecting        the application.

FIG. 12 illustrates in flowchart form an example embodiment of a process1200 to provide a wireless network with fault tolerance. At 1205, anassessment is made on the effect of a communication degradation betweenany of the logical communication entities of the network. At 1210, thenetwork infrastructure is configured based on that assessment. In thisprocess 1200, the infrastructure includes redundant wirelesscommunication between the logical communication entities, therebyproviding the fault tolerance within the network. At 1215, the redundantwireless communication involves wirelessly communicating to a logicalaccess entity of the logical communication entity, and at 1220, theredundant wireless communication involves wirelessly communicating to anode entity of the logical communication entity. In the process 1200,the logical communication entity may be within a BSS of the wirelessnetwork or an ESS of the wireless network, and the logical access entitymay include a wireless network interface card. At 1225, a plurality ofnon-overlapping communication channels is provided to the logicalcommunication entity. At 1230, the redundant wireless communicationchannel is selected as a function of communication signal parameters.These communication signal parameters may include one or more of asignal to noise ratio, a received signal strength, network trafficdensity, and an acknowledgment of a failure. Further, at 1235, theredundant wireless communication channel is selected as a function ofavailability of one or more synchronization signals transmitted from oneor more of the logical access entities. At 1240, a redundantcommunication path is established among the logical communicationentities. The logical communication entities may include middleware thatis configured to recognize communication degradation associated with anyof the communication entities. The middleware may further be configuredto switch communication among the logical communication entities.

FIG. 13 is an overview diagram of a hardware and operating environmentin conjunction with which embodiments of the invention may be practiced.The description of FIG. 13 is intended to provide a brief, generaldescription of suitable computer hardware and a suitable computingenvironment in conjunction with which the invention may be implemented.In some embodiments, the invention is described in the general contextof computer-executable instructions, such as program modules, beingexecuted by a computer, such as a personal computer. Generally, programmodules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types.

Moreover, those skilled in the art will appreciate that the inventionmay be practiced with other computer system configurations, includinghand-held devices, multiprocessor systems, microprocessor-based orprogrammable consumer electronics, network PCS, minicomputers, mainframecomputers, and the like. The invention may also be practiced indistributed computer environments where tasks are performed by I/0remote processing devices that are linked through a communicationsnetwork. In a distributed computing environment, program modules may belocated in both local and remote memory storage devices.

In the embodiment shown in FIG. 13, a hardware and operating environmentis provided that is applicable to any of the servers and/or remoteclients shown in the other Figures.

As shown in FIG. 13, one embodiment of the hardware and operatingenvironment includes a general purpose computing device in the form of acomputer 20 (e.g., a personal computer, workstation, or server),including one or more processing units 21, a system memory 22, and asystem bus 23 that operatively couples various system componentsincluding the system memory 22 to the processing unit 21. There may beonly one or there may be more than one processing unit 21, such that theprocessor of computer 20 comprises a single central-processing unit(CPU), or a plurality of processing units, commonly referred to as amultiprocessor or parallel-processor environment. In variousembodiments, computer 20 is a conventional computer, a distributedcomputer, or any other type of computer.

The system bus 23 can be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. The system memorycan also be referred to as simply the memory, and, in some embodiments,includes read-only memory (ROM) 24 and random-access memory (RAM) 25. Abasic input/output system (BIOS) program 26, containing the basicroutines that help to transfer information between elements within thecomputer 20, such as during start-up, may be stored in ROM 24. Thecomputer 20 further includes a hard disk drive 27 for reading from andwriting to a hard disk, not shown, a magnetic disk drive 28 for readingfrom or writing to a removable magnetic disk 29, and an optical diskdrive 30 for reading from or writing to a removable optical disk 31 suchas a CD ROM or other optical media.

The hard disk drive 27, magnetic disk drive 28, and optical disk drive30 couple with a hard disk drive interface 32, a magnetic disk driveinterface 33, and an optical disk drive interface 34, respectively. Thedrives and their associated computer-readable media provide non volatilestorage of computer-readable instructions, data structures, programmodules and other data for the computer 20. It should be appreciated bythose skilled in the art that any type of computer-readable media whichcan store data that is accessible by a computer, such as magneticcassettes, flash memory cards, digital video disks, Bernoullicartridges, random access memories (RAMs), read only memories (ROMs),redundant arrays of independent disks (e.g., RAID storage devices) andthe like, can be used in the exemplary operating environment.

A plurality of program modules can be stored on the hard disk, magneticdisk 29, optical disk 31, ROM 24, or RAM 25, including an operatingsystem 35, one or more application programs 36, other program modules37, and program data 38. A plug in containing a security transmissionengine for the present invention can be resident on any one or number ofthese computer-readable media.

A user may enter commands and information into computer 20 through inputdevices such as a keyboard 40 and pointing device 42. Other inputdevices (not shown) can include a microphone, joystick, game pad,satellite dish, scanner, or the like. These other input devices areoften connected to the processing unit 21 through a serial portinterface 46 that is coupled to the system bus 23, but can be connectedby other interfaces, such as a parallel port, game port, or a universalserial bus (USB). A monitor 47 or other type of display device can alsobe connected to the system bus 23 via an interface, such as a videoadapter 48. The monitor 40 can display a graphical user interface forthe user. In addition to the monitor 40, computers typically includeother peripheral output devices (not shown), such as speakers andprinters.

The computer 20 may operate in a networked environment using logicalconnections to one or more remote computers or servers, such as remotecomputer 49. These logical connections are achieved by a communicationdevice coupled to or a part of the computer 20; the invention is notlimited to a particular type of communications device. The remotecomputer 49 can be another computer, a server, a router, a network PC, aclient, a peer device or other common network node, and typicallyincludes many or all of the elements described above I/0 relative to thecomputer 20, although only a memory storage device 50 has beenillustrated. The logical connections depicted in FIG. 13 include a localarea network (LAN) 51 and/or a wide area network (WAN) 52. Suchnetworking environments are commonplace in office networks,enterprise-wide computer networks, intranets and the internet, which areall types of networks.

When used in a LAN-networking environment, the computer 20 is connectedto the LAN 51 through a network interface or adapter 53, which is onetype of communications device. In some embodiments, when used in aWAN-networking environment, the computer 20 typically includes a modem54 (another type of communications device) or any other type ofcommunications device, e.g., a wireless transceiver, for establishingcommunications over the wide-area network 52, such as the internet. Themodem 54, which may be internal or external, is connected to the systembus 23 via the serial port interface 46. In a networked environment,program modules depicted relative to the computer 20 can be stored inthe remote memory storage device 50 of remote computer, or server 49. Itis appreciated that the network connections shown are exemplary andother means of, and communications devices for, establishing acommunications link between the computers may be used including hybridfiber-coax connections, T1-T3 lines, DSL's, OC-3 and/or OC-12, TCP/IP,microwave, wireless application protocol, and any other electronic mediathrough any suitable switches, routers, outlets and power lines, as thesame are known and understood by one of ordinary skill in the art.

In the foregoing detailed description of embodiments of the invention,various features are grouped together in one or more embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimedembodiments of the invention require more features than are expresslyrecited in each claim. Rather, as the following claims reflect,inventive subject matter lies in less than all features of a singledisclosed embodiment. Thus the following claims are hereby incorporatedinto the detailed description of embodiments of the invention, with eachclaim standing on its own as a separate embodiment. It is understoodthat the above description is intended to be illustrative, and notrestrictive. It is intended to cover all alternatives, modifications andequivalents as may be included within the scope of the invention asdefined in the appended claims. Many other embodiments will be apparentto those of skill in the art upon reviewing the above description. Thescope of the invention should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. In the appended claims, the terms“including” and “in which” are used as the plain-English equivalents ofthe respective terms “comprising” and “wherein,” respectively. Moreover,the terms “first,” “second,” and “third,” etc., are used merely aslabels, and are not intended to impose numerical requirements on theirobjects.

The abstract is provided to comply with 37 C.F.R. 1.72(b) to allow areader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

1. A network comprising: a plurality of logical access entities, eachaccess entity including two or more communication interfaces; and aplurality of logical node entities, each logical node entity includingtwo or more communication interfaces configured to wirelesslycommunicate in a redundant manner with any of said logical accessentities; wherein non-overlapping communication channels are establishedalong redundant communication paths among the two or more logical accessentities and the two or more logical node entities using the two or morecommunication interfaces of the logical access entities and the two ormore communication interfaces of the logical node entities; wherein saidtwo or more communication interfaces comprise wireless interface cards;and wherein said redundant wireless communication paths are selected asa function of communication signal parameters, said communication signalparameters including one or more of a signal to noise ratio, a receivedsignal strength, network traffic density, and an acknowledgment of afailure; and wherein said redundant wireless communication paths areselected as a function of availability of one or more synchronizationsignals transmitted from one or more logical access entities.
 2. Thenetwork of claim 1, wherein each logical node entity is configured to beassociated with one or more of the logical access entities.
 3. Thenetwork of claim 2, wherein said logical node entity is within anextended service set of said network.
 4. The network of claim 2, whereinsaid logical node entity is within a basic service set of said network.5. The network of claim 1, wherein one or more of said logical accessentities and said logical node entities comprise middleware configuredto recognize communication degradation associated with any of saidlogical access entities and said logical node entities.
 6. The networkof claim 5, wherein said middleware is configured to switchcommunication among said logical access entities and said logical nodeentities.
 7. A system comprising: a plurality of logical accessentities, each access entity having two or more communicationinterfaces; and a plurality of logical node entities, each logical nodeentity having two or more communication interfaces adapted to wirelesslycommunicate in a redundant fashion with any of said logical accessentities; wherein non-overlapping communication channels are establishedalong redundant communication paths among the logical access entitiesand the logical node entities using the two or more communicationinterfaces of the logical access entities and the two or morecommunication interfaces of the logical node entities; and wherein saidredundant wireless communication paths are selected as a function ofcommunication signal parameters, said communication signal parametersincluding one or more of a signal to noise ratio, a received signalstrength, network traffic density, and an acknowledgment of a failure;and wherein said redundant wireless communication paths are selected asa function of availability of one or more synchronization signalstransmitted from one or more logical access entities.
 8. The system ofclaim 7, wherein each logical node entity is configured to be associatedwith any of the logical access entities.
 9. The system of claim 7,wherein the communication interfaces comprise wireless interface cards.10. The system of claim 7, wherein said logical node entities are withinan extended service set of said system.
 11. The system of claim 7,wherein said logical node entities are within a basic service set ofsaid system.
 12. The system of claim 7, wherein one or more of saidlogical access entities and said logical node entities comprisesmiddleware configured to recognize communication degradation associatedwith any of said logical access entities and said logical node entities.13. The system of claim 12, wherein said middleware is configured toswitch communication among said logical access entities and said logicalnode entities.
 14. A network comprising: a plurality of logical accessentities, each access entity including two or more communicationinterfaces; and a plurality of logical node entities, each logical nodeentity including two or more communication interfaces configured towirelessly communicate in a redundant manner with any of said logicalaccess entities; wherein non-overlapping communication channels areestablished along redundant communication paths among the two or morelogical access entities and the two or more logical node entities usingthe two or more communication interfaces of the logical access entitiesand the two or more communication interfaces of the logical nodeentities; wherein said two or more communication interfaces comprisewireless interface cards; and wherein said redundant wirelesscommunication paths are selected as a function of communication signalparameters, said communication signal parameters including one or moreof a signal to noise ratio, a received signal strength, network trafficdensity, and an acknowledgment of a failure; and wherein said redundantwireless communication paths are selected as a function of availabilityof one or more synchronization signals transmitted from one or morelogical access entities.
 15. The network of claim 14, wherein eachlogical node entity is configured to be associated with one or more ofthe logical access entities.
 16. The network of claim 15, wherein saidlogical node entity is within an extended service set of said network;and wherein said logical node entity is within a basic service set ofsaid network.
 17. The network of claim 14, wherein one or more of saidlogical access entities and said logical node entities comprisemiddleware configured to recognize communication degradation associatedwith any of said logical access entities and said logical node entities.18. The network of claim 17, wherein said middleware is configured toswitch communication among said logical access entities and said logicalnode entities.